Microminiaturized minimally invasive intravascular micro-mechanical systems powered and controlled via fiber-optic cable

ABSTRACT

A micro-mechanical system for medical procedures is constructed in the basic form of a catheter having a distal end for insertion into and manipulation within a body and a near end providing for a user to control the manipulation of the distal end within the body. A fiberoptic cable is disposed within the catheter and having a distal end proximate to the distal end of the catheter and a near end for external coupling of laser light energy. A microgripper is attached to the distal end of the catheter and providing for the gripping or releasing of an object within the body. A laser-light-to-mechanical-power converter is connected to receive laser light from the distal end of the fiberoptic cable and connected to mechanically actuate the microgripper.

The United States Government has rights in this invention pursuant toContract No. W-7405-ENG48 between the United States Department of Energyand the University of California for the operation of Lawrence LivermoreNational Laboratory.

CO-PENDING APPLICATIONS

This Application is a continuation-in-part of U.S. patent applicationSer. No. 08/446,146, filed May 22, 1995, docket number IL-9193, andtitled MICROFABRICATED THERAPEUTIC ACTUATOR now U.S. Pat. No. 5,645,564MECHANISMS; U.S. patent application Ser. No. 08/533,426, filed Sep. 25,1995, docket number IL-9681, and titled MICROMACHINED ACTUATORS/SENSORSFOR INTRATUBULAR POSITIONING/STEERING; and, U.S. patent application Ser.No. 08/549,497, filed Oct. 27, 1995, docket number IL-9729, and titledMINIATURE PLASTIC GRIPPER AND FABRICATION METHOD. All such Applicationsare incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to remote sensors and actuators, andparticularly to microminiaturized electro-mechanical microgrippers foruse in catheter-based interventional therapies or in non-medical remotemicro-assembly applications. Such applications have in common very smallaccess ports, and very small operational chamber areas that are burieddeep within a body or assembly.

Microactuators for remote and precise manipulation of small objects isof great interest in a wide variety of applications. The design anddevelopment effort of such microgripper devices would be useful in theart as such will apply to general microfabrication techniques andestablish the infrastructure for microengineering efforts includingrobotics, microtechnology, prevision engineering, defense, energy, andbiomedical research, as well as use in medical applications, such as forcatheter-based interventional therapies and remote assembly or use ofmicromechanical system.

When a portion of a blood vessel weakens, it bulges and forms aaneurysm, which is one of the main reasons for strokes as the vesselfinally collapses and opens. These aneurysms have traditionally beentreated by surgery, where the surgeon will have to open up the area ofrepair before attempting to surgically repair the aneurysm by clippingit. However, many aneurysms are at critical locations such as in thebrain and are either difficult and risky to operate on or it is simplyimpossible. For the last 20 years, pioneering doctors have usedinterventional neuroradiology techniques to aid the treatment of brainaneurysms. Long (1-2 meters) and narrow (i.e. 250 μm to 500 μm)catheters are pushed through the arteries in the groin up to the brainto reach the aneurysm. Existing catheter-based interventionalinstruments rely on simplistic and usually singular means of actuation.These techniques, including balloon angioplasty, are well-establishedfor large vessel treatments such as in the heart. It is crucial that inorder to extend this medical practice into the smaller vessels such asthose in the brain, the catheter-based tools must be miniaturized. Inthe most recent method, platinum coils were selected to fill up theaneurysms due to its ability to fill up irregular shapes and itsresistance to electrolysis in the vessels when it is charged. The coilsare either pushed through the catheter to the aneurysm by a guide wireor released by the electrolytic dissolution of a solder joint betweenthe guide wire of the catheter and the therapeutic device, which forneurological treatments are approximately 250 μm or less in diameter.Although the charging of the coil causes electrothrombosis around thecoil, the time required to release the coil is long (4 mins to 1 hr) andmany coils are usually needed to fill up a regular size aneurysm. Theextent to which the dissolved material affects the body is unknown andelectrolysis soldering requires long terms of current in the brain andsometimes is simply unreliable. These difficulties present potentiallife-threatening problems to the patient for the surgeon and clinician.

Thus, there is a need for a micromechanism which can fit into a 250 μmdiameter area and which would enable the physician to release andretrieve the coils or other therapy once it is released at the wrongtime or location. The present invention satisfies this need by providinga micromechanical release mechanism by which this procedure becomes asafer and more reliable alternative to surgery, and which can fit intoblood vessels of the brain, a 250 μm diameter area. Theelectromechanical microstructures, including microgrippers, can befabricated using known IC silicon-based techniques or precisionmicromachining, or a combination of these techniques. While theinvention has application in various areas requiring a remotely actuatedmicrogripper, it has particular application in catheter-basedinterventional therapies.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an electromechanicalmicrogripper.

A further object of the invention is to provide a microgripper with alarge gripping force, a relatively rigid structural body, andflexibility in function design.

A further object of the invention is to provide an electromechanicalmicromechanism mounted at one end of a catheter and which can bemanipulated from the other end, thereby extending and improving theapplication of catheter-based interventional therapies.

Another object of the invention is to provide a microgripper capable ofoperating in an area as small as a 250 μm diameter, such as in the bloodvessels of the brain.

Another object of the invention is to provide a microgripper which canbe used to integrate heaters and strain sensors for remote activeheating and feedback control.

Another object of the invention is to provide a microgripper which canbe used as a biopsy tissue sampler, or for use as a tip designed forhandling microparts.

Another object of the invention is to provide a microgripper which hasthe potential to apply alternative actuation mechanisms, eitherhydraulic or simply thermal bimorphic.

Another object of the invention is to provide a microgripper with alarge gripping force (40 mN), wherein actuation thereof is generated byshape-memory alloy thin films and the stress induced can deflect eachside of a microgripper up to about 55 μm for a total gripping motion ofabout 110 μm.

Briefly, an embodiment of the present invention is micromechanicalsystem for medical procedures. The system is constructed in the basicform of a catheter having a distal end for insertion into andmanipulation within a body and a near end providing for a user tocontrol the manipulation of the distal end within the body. A fiberopticcable is disposed within the catheter and having a distal end proximateto the distal end of the catheter and a near end for external couplingof laser light energy. A microgripper is attached to the distal end ofthe catheter and providing for the gripping or releasing of an objectwithin the body. A laser-light-to-mechanical-power converter isconnected to receive laser light from the distal end of the fiberopticcable and connected to mechanically actuate the microgripper.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the disclosure, illustrate embodiments of the invention and, togetherwith the description, serve to explain the principles of the invention.

FIGS. 1A and 1B are cross-sectional views of an embodiment of themicrogripper using balloon activation, and shown in the closed and openpositions.

FIG. 2 is an exploded view of the FIGS. 1A-1B embodiment, with theballoon omitted.

FIGS. 3A and 3B illustrate another embodiment of the microgripper usinga thin film tweezer-like activator.

FIGS. 4A and 4B are cross-sectional views which illustrate anotherembodiment of the microgripper using a shape-memory alloy (SMA) wireclicker.

FIG. 5 is an exploded view of the FIGS. 4A-4B embodiment with the SMAwire omitted.

FIG. 6 is an embodiment of the invention using SMA double coils.

FIG. 7 is a preferred embodiment of a silicon microgripper made inaccordance with the present invention.

FIG. 8 is a cross-sectional view illustrating the eutectic bondingprocess.

FIGS. 9A, 9B and 9C illustrate resistive heaters and electricalfeedthrough for FIG. 7 a microgripper.

FIGS. 10, 10A and 10B illustrate an embodiment of the heater of FIG. 8A,with cross-sections as shown in FIGS. 10A and 10B greatly enlarged.

FIGS. 11, 11A and 11B illustrate another embodiment of the heater ofFIG. 9A, with the cross-sections of FIGS. 11A and 11B greatly enlarged.

FIG. 12 illustrates a force feedback control system for the microgripperof FIG. 7.

FIG. 13 is a view of an SMA film activated microactuator made inaccordance with the invention for providing hydraulic pressure/fluiddelivery from a microballoon.

DETAILED DESCRIPTION OF THE INVENTION

The invention is an electromechanical grip/release micromechanismreferred to herein as a microgripper or microclamper. The microgripperhas a large gripping force, a relatively rigid structural body, andflexibility in functional design such that it can be used, for example,as a biopsy tissue sampler, a tip designed for handling microparts, oras a release/retrieval mechanism for items such as platinum coils orother materials in bulging portions of the blood vessels, known asaneurysms. The microgripper of this invention is particularly useful toextend and improve the application of catheter-based interventionaltherapies, and is capable of use in a 250 μm diameter area, such as asmall blood vessel of the brain. The microgripper may be constructedwith outer surfaces which can be used to integrate heaters or strainsensors for remote active heating and feedback control. One embodimentof the microgripper, for example, is of a silicon structure andincorporates shape-member alloy (SMA) thin films, and the stress inducedcan deflect the sides thereof to enable a gripping motion of about 110μm. The microgripper can be fabricated by precision micromachining or bytechniques utilized in the fabrication of silicon-based integratedcircuits.

The ultimate objective of the grip/release mechanism or microgripper isto achieve the following: 1) the cross-section should fit into adiameter as small as a 250 μm area (open and closed); 2) the release ofmaterials into the blood vessels should be less than 10 seconds; 3) thetemperature range should be between 0° C. and 37° C.; 4) current shouldbe less that 10 mA, for example, if electrical energy is used; 5) 100%reliability.

Using conventional silicon bulk micromachining techniques a mechanicalclamper or microgripper as illustrated in FIGS. 1A, 1B, and 2 can befabricated to include a cantilever structure therein which, for example,is about 800 μm in length and the total height of the structure is 250μm. Then a silicon microballoon may be utilized to mechanically deflectthe cantilever arms to clamp onto foreign objects at the front endthereof, as seen in FIGS. 1A and 1B. The microballoons are wellcharacterized and can withstand pressures of up to 10 atm. Suchmicroballoons have also been tested for use in human blood vessels. Asseen in FIGS. 1A-1B and FIG. 2, the balloon activated microgrippergenerally indicated at 10 comprises a pair of jaws, grip arms, orgripping members 11 and 12, each having a plurality of slottedcantilevers 13 and 14, a pusher pad 15 and 16, and grippers 17 and 18.For some applications the pusher pads may be omitted. The jaws orgripping members 11 and 12 are bonded or otherwise secured together asindicated at 19. An expandable device, such as a balloon 20, ispositioned between gripping members 11 and 12 and connected to adelivery tube or catheter 21 which extends along the balloon path 22(See FIG. 2) through which an activating fluid or gas is supplied toactivate (expand) the balloon 20. Pusher pads 15 and 16 serve as balloonforce points 23 (See FIG. 2), and when fully expanded an end of theballoon may extend between the pusher pads 15-16 as shown in FIG. 1A.

With the balloon 20 in inactivated (unexpanded) position as shown inFIG. 1A, the grippers 15 and 16. Upon activation enlargement of theballoon 20, the outer ends of gripping members 11 and 12 bend or flexoutwardly at the location of slotted cantilevers 13 and 14 causing thegrippers 17 and 18 to separate, allowing the material 24 retainedtherebetween to be removed therefrom, as shown in FIG. 1B.

The gripper members 11 and 12 may be constructed of silicon, aluminum,nickel or other compatible metals, Teflon or other compatible polymers,and ceramics with a length of 0.8 mm to 1.5 mm, and a width and combinedheight preferably not greater than about 250 μm. The balloon 20 may be asilicone microballoon capable of withstanding pressures of up to 10atmospheres, supplied through the tube 21, which may be constructed ofTeflon or other inert plastics having a diameter of 80 μm to 400 μm. Theballoon 20 may be replaced with other expandable devices. The bond 19may be formed, for example, by selective eutectic bonding. The pusherpads 15 and 16 have, for example, a thickness of 20 μm to 40 μm, andgrippers 17 and 18 may have a thickness of 90 μm to 150 μm and length of50 μm to 150 μm. The slotted cantilevers 13 and 14 may be composed of 3to 10 slots having a width of 5 μm to 100 μm and length of 50 μm to 500μm. The slots of the cantilevers may be straight or tapered along thelength thereof. The material that the gripper members 11 and 12 isconstructed from must be inert to the fluid or chemicals involved.

The embodiment of FIGS. 3A and 3B utilizes a pair of initial SMA thinfilm hinges to open and close the grip arms or gripping membersaccording to the temperature the SMA thin film is exposed to. The SMAthin films of FIGS. 3A and 3B can also be replaced by a heatersandwiched by polyimide layer expands and deflects the cantileverclampers or grippers.

As shown in FIGS. 3A and 3B, the microgripper, generally indicated at 30is composed of a pair of grip arms or gripping members 31 and 32 formed,for example, from silicon wafers, and each included a reduced thicknessof cross-section area 33 and 34 and a pair of inwardly directed spacedgrippers 35 and 36 only one gripper of each pair being shown, whichretain a material or part 37, such as a stem of a platinum cell (SeeFIG. 3A). Thin films 38 and 39 are secured to gripping members 31 and 32adjacent the reduced areas 33 and 34, with films 38 and 39 beingconstructed of SMA or polyimide layers as described above. The grippingmembers 31 and 32 are also provided with pusher pads 40 and 41. Uponheating of the thin films 38 and 39 by a heater, not shown, the filmsexpand causing outward flexing or bending of the outer ends of grippingmembers 31 and 32 at areas 33 and 34 causing the grippers 35 and 36 toseparate (See FIG. 3B) whereby material 37 is removed therefrom.

By way of example, the grip arms or gripping members 31 and 32 may beconstructed of silicon, or compatible metals, polymers, or ceramics withan overall combined height and width thereof preferably not to exceed250 μm, with the thickness of members 31 and 32 being 20 to 100 μ, withreduced areas 33 and 34 having a thickness of 5 to 15 μm, and grippers35 and 36 extending inwardly from members 31 and 32 a distance of 20 to50 μm. The pusher pads 40 and 41 may for example, having a thickness of20 to 40 μm and depth (height) of 30 to 100 μ. The thin films 38 and 39,if constructed of SMA, may be composed of Ni--Ti, Ni--Ti--Cu, or otherlow temperature SMA, having a thickness of 2 to 5 μm, and if composed ofpolyimide, for example, having two layers of a thickness of 3 to 10 μmand length of 300 μm to 500 μm, which sandwich therebetween a heaterconstructed of Ti--Au. Heating of the SMA films 38 and 39 isaccomplished, for example, by integrating polysilicon heaters or directresistive heaters of SMA, as described hereinafter with respect to FIGS.9 and 10, or by laser heating through optical fibers. Shape-memoryalloys are well known, as evidenced by U.S. Pat. No. 5,061,914 issuedOct. 29, 1991 to J. D. Busch, et al.

The embodiment of FIGS. 1A-1B and 3A-3B can also be utilized to retrievematerial or parts, such as platinum coils used to repair aneurysms.These embodiment have advantages over prior known microgrippers that areelectrically conductive (see C. J. Kim et al, "Silicon-ProcessedOverhanging Microgripper", Journal of Microelectromechanical Systems,Vol. 1, No. 1, pp. 31-36, March 1992) and can be used to manipulatebiological cells or micro parts for assembly.

The embodiment of FIGS. 4A-4B and FIG. 5 is a microgripper that is anormally open release mechanism (FIG. 4B), where an SMA wire is used asa latch to close the microgripper (FIG. 4A), and when activated to clickopen the mechanism. As shown, this embodiment, generally indicated at50, comprises a pair of grip arms or gripping members 51 and 52,generally similar in construction to the gripping members 11 and 12 ofthe FIGS. 1A-1B embodiment, and are provided with hook connectors 53 and54, pusher pads 55 and 56, and pairs of grippers 57 and 58, only oneeach shown. A compressive thin film 59 and 60 is secured in openings 61and 62 of gripping members 51 and 52. Hook connectors 53 and 54 haveopening 63 and 64 (see FIG. 5) through which an SMA wire 65 extends (seeFIG. 4A) to "close" the gripping members 51 and 52 and compress thecompressive thin films 59 and 60. Upon activation of the SMA wire 65,the wire is withdrawn from openings 63 and 64 of hook connector s 53 and54, as indicated by the arrows 66 (see FIG. 4B), whereupon thecompressive thin films 59 and 60 expand causing the ends of grippingmembers 51 and 52 to flex or bend outwardly. In the closed position (seeFIG. 4A) the pairs of grippers 57 and 58 retain a material or part 67therebetween, and upon activation or clicking open of the latch (hookconnectors 53 and 54 and SMA wire 65), the grippers 57 and 58 moveoutwardly allowing the material or part 67 to be removed fromtherebetween. As in the embodiment of FIGS. 1A-1B, the gripping members51 and 52 are bonded together as indicated at 68.

By way of example, the gripping members 51 and 52, pusher pads 55 and56, and grippers 57 and 58 may be constructed and configured asdescribed above in the FIGS. 1A-1B embodiment. The hook connects 53 and54 are composed of silicon, metals, polymers or ceramics and secured, asby micromachining, and having a height of 80 to 200 μm, width of 200 to500 μm and the openings 63 and 64 therein have a cross-section of 80 to380 μm, width of 180 to 480 μm, and may be configured other than square.The SMA wire 65 may be composed of Ni--Ti--Cu, Ni--Ti, or Ni--Ti--Hf,having a cross-section and configuration which corresponds with theopenings 63 and 64 of hook members 53 and 54. The compressive thin film59 and 60 may be constructed of silicon dioxide, doped polysilicon, orpolymers having a thickness of 3 to 8 μm, and cross-section of 250×250or 250×400 μm.

FIG. 6 illustrates a microgripper using two SMA micro-coils, one to gripon to the stem of a platinum coil, for example, and the other one topush the platinum coil outwards to assure the release, the micro-coilsbeing secured at one end to the tip of a guide wire, such as used incatheter-based interventional therapies. As shown in FIG. 6, two SMAcoils 170 and 171 are secured at one end to a guide wire 172. Coil 170,of substantially greater cross-section and of greater diameter than coil171, extends (wraps around coil 171 and around an end of a stem 173 of aplatinum cell, for example, and retains or grips the stem 173. The coil171 extends between the tip 179 of guide wire 172 and end 175 of stem173. Under normal conditions the coil 170 retains the stem 173 frommoving, and upon activation the coil 171 expands pushing the stem 173out of the coil 170.

By way of example, the larger coil 170 may be constructed of SMA wirehaving a diameter of 50 to 75 μm, a number of turns or wraps rangingfrom 10 to 15, and constructed of Ni--Ti, Ni--Ti--Cu, or Ni--Ti--Hf. Thesmaller coil 171 may be constructed of SMA wire composed of Ni--Ti,Ni--Ti--Cu, and Ni--Ti--Hf, having a diameter of 30 to 50 μm, with theturns or wraps ranging from 5 to 10. The micro-coils 170 and 171 may besecured to guide wire 172 by bonding, soldering, etc.

The preferred embodiment of FIG. 7 uses a combination of siliconstructure and SMA thin film, and is provided with a wiring jacket forsignal input. This embodiment provides a microgripper that can belocally actuated at low temperatures (<100° C.), with a large grippingforce (10 to 40 mN), a relatively rigid structural body, and flexibilityin functional design. Also, this microgripper has the capability to lockthe target gripping object. The actuation of the microgripper isgenerated, for example, by NiTiCu shape-memory alloy thin films and thestress induced can deflect each side of the microgripper up to 55 μm fora total gripping motion of 110 μm. This opening motion corresponds to a20 mN opening force on the tip of the gripper. In addition themicrogripper can work in a liquid environment. The opening jaws, thepusher pads, and the hollow channel are shaped by a combination ofprecision sawing and bulk machining of silicon. Two preprocessed siliconwafers are prevision aligned and selectively bonded, using an Au--Sieutectic process which involves aligning a mask on a wafer andevaporating through the mask onto the gripper bonding portion, asdescribed in greater detail hereinafter with respect to FIG. 8. Themicrogripper of FIG. 7 is 1 mm×200 μm×380 μm in dimension, having a pairof silicon cantilevers 12.5 μm thick, with 5 μm thick NiTiCu SMA thinfilms deposited on the outer sides of the cantilevers or gripper arms toprovide actuation of the microgripper. The SMA thin film can generateactuation stresses up to 500 MPa at transformation temperatures between30° C. to 70° C., which is a lower temperature than all known thermalbimorphic microgrippers. For experimental verification, the microgripperwas actuated by external heating and a video tape was prepared todemonstrate the opening and closing motions.

Referring now to a specific embodiment as shown in FIG. 7, themicrogripper generally indicated at 70 includes a pair of siliconcantilevers, gripper arms or gripping members 71 and 72, each member 71and 72 having a 30 μm wide pusher pad indicated at 73 and 74,respectively, and a pair of 60×110×100 μm³ gripping jaws or grippers 75and 76. The gripping members 71 and 72 are Au--Si eutectic bondedtogether at an interface 77, and are each provided with an SMA thin film78 and 79 on the outer surfaces or sides thereof. The cantilevers orgripping members 71 and 72 are constructed to define a 110 μm widehollow channel 80 in the area of the bonded interface 77, which is incommunication with one end of a catheter, for example, on which themicrogripper is mounted. The microgripper 70 is secured to a wiringjacket, generally indicated at 81, for signal inputs.

The composition of the gripping members 71 and 72, the SMA thin films 78and 79, the eutectic bond 77, and the dimensions of the microgripper 70have been set forth above. By way of example, the pusher pads 73 and 74may have a thickness of 20 to 40 μm and height of 80 to 100 μm; with thegripper 75 and 76 having a height of 80 to 100 μm, and end cross-sectionof 70×150 μm; and with the hollow channel 80 having a width of 100 to250 μm and height of 50 to 180 μm.

The fabrication of the microgripper embodiments of FIGS. 1A-1B, 3A-3B,4A-4B, and 7, particularly FIG. 7, allows the designer some flexibilityin shaping the gripping jaws as the targeting specimens dictate, and caneither be used as a biopsy tissue sampler or a catheter tip designed forhandling microparts. The outer surfaces of the microgripper,particularly FIG. 7, can be used to integrate heaters or strain sensorsfor remote active heating and possible feedback control as describedhereinafter with respect to FIGS. 9-12. The hollow channel of the FIG. 7embodiment has the potential for either wire connection or injection ofliquids and therapeutic medicine. Another important advantage is thepossibility to apply alternative actuation mechanisms on themicrogripper structure, either hydraulic or simply thermal bimorphic.Many creative designs of practical microgrippers for variousapplications can be conceived using this basic approach. Fabricationprocess steps can be highly automated and batch fabrication of themicrogrippers will reduce the manufacturing cost.

Applications of the FIG. 7 microgripper include assembling small partsfor manufacturing, minimally-invasive in vivo biopsy tissue sampling,catheter-based endovascular therapeutic procedures, and remote handlingof small particles in extreme environments (high/low pressures,hazardous fluids, etc.).

The microfabrication process for the FIG. 7 embodiment can becategorized into bulk micromachining, fine alignment, etching, andNi--Ti--Cu SMA thin film deposition. As set forth above, a specificembodiment of the FIG. 7 type microgripper is 1000×200×380 μm³ indimension. Each silicon cantilever (72 and 73) is 125 μm thick and 5 μmNi--Ti--Cu SMA thin films (78 and 79) are deposited on the outersurfaces of the cantilevers for actuation thereof. The pusher pads(73-74) are 30 μm wide while the gripping jaws (75-76) are 60×110×100μm³. The hollow channel 80 is 110 μm wide and 175 μm in height. Thegripping jaws, pusher pads, and hollow channel are shaped by acombination of precision sawing and bulk machining of silicon, and thuscan be batch fabricated. The connection of the microgripper to externalleads and milli-end effectors (as exemplified in FIG. 9) requiresassembly and therefore does not allow for batch fabrication. However,there is an ongoing effort to develop assembly techniques for packaging.

The cantilevers or gripper arms (71-72) of the microgripper arefabricated on two silicon wafers. This process starts with two 100 μmthick (110) p-type silicon wafers, which are ground and polished from awidth of 200 μm to an overall width of 380 μm. The common masking filmfor patterning and etch silicon was 1000 Å of silicon nitride.

A test pattern is essential to identify the exact (111) plane as opposedto the wafer flat, which is typically offset 2°-3°. Alignment targetsare imprinted on each of the silicon wafers using this crystal planeidentifying pattern to ensure the subsequent aligning to the exactcrystal planes. Two types of alignment targets must be defined, one tocarry out front-to-back alignment and another etched through the wafersto provide holes for precise pin mechanical alignments for eutecticbonding. Dicing line (2 μm deep) are then patterned on the backside ofeach wafer. On the front side of each wafer, saw cut channel guide linesare patterned for the precision saw to form the silicon cantilevers(71-72) and the pusher pads (73-74). These patterns are imprinted byetching the silicon down 1 μm. After reapplying the masking siliconnitride, lathography is carried out for the gripping jaws (75-76) andthe hollow channel (80). The silicon wafers are then etched in 44% KOH,creating vertical walls 85 μm deep. The silicon nitride mask is thenstripped and ready for the precision saw, such as a model 780 by Kulicke& Sofia, with positioning accuracy as high as 2.5 μm. Precision sawingwas chosen to avoid the anisotropic etching limitations of silicon thatdoes not allow vertical wall etch channels 90° apart without carefulcorner compensation and sacrifice of finished surfaces. Since the widthof the two cut channels are 200 μm and 400 μm, respectively, the bladeselected was 200 μm thick. The wider cut channel (400 μm) was formed bymaking two adjacent saw cuts. The saw was indexed to leave a pusher pad(73-74) width of 30 μm. For careful control of the cut depths, it isnecessary to index the depth from the bottom of the wafer. Furthermore,it is ideal to dress the blades on rougher surfaces to achieve thevertical edges. The pair of silicon cantilevers or gripper arms (71-72)formed from the silicon wafers are now reading for bonding.

Bonding of the cantilever or gripper arms of FIG. 7, for example, iscarried out using Au--Si eutectic bonding, whereby selective areas ofbonding at a low temperature (<400° C.) is achieved. The siliconmicrostructures, such as the gripper arms of FIG. 7 can be bulkmicromachined on two silicon wafers, as described above, and theneutectic bonded, which enables designer to designer minimal gapmicrostructures that can also be applied as capacitancesensors/actuators and microfluidics systems with tight seals.

Using Au--Si eutectic bonding a microstructure, composed of the twosilicon machined wafers, such as illustrated in FIG. 7 may be fabricatedas illustrated in FIG. 8. On each cantilever 82 framed from a siliconwafer, Ti/Au pads, generally indicated at 83, 500×500 μm in area forexample, are deposited by electron beam (E-Beam) evaporation indicatedat 84, by arrows and patterned through shadow masks 85 and 86, such asillustrated in FIG. 8. The Ti layer 87 is an adhesive layer and alsoserves as a diffusion barrier for Au layer 88. The thickness of the pads83 are, for example, 500 Å for Ti (layer 87) and 1 μm for Au (layer 88).The annealing temperature is 370° C. to 390° C. which is above the 363°C. eutectic point to assure the interface to liquidify. Soaking at thistemperature for 5 minutes is necessary. The shadow masks 85-86 arecurrently fabricated by etching windows out of (100) silicon wafers. Byaligning the shadow masks to the wafer only areas coated with Ti/Au willbe bonded together. The mating silicon wafers should have a fullycleaned silicon surface where the bonding is to occur. The wafers arethen pressurized together and held in low vacuum (nominally 10⁻⁴ Torr)and soaked, for example, at 380° C. for three (3) minutes. An acousticimage of an array of Ti/Au eutectic bonding pads 83 seen through a pairof 2 inch silicon wafers showed that a highly uniform and solid bond hasbeen formed. The Au--Si bond strength was measured in an instron pulltest, where 9 eutectic bond pads were pulled and failed at pull stressof 5.5 GPa. The eutectic bond areas were intact, as fracturing of thesilicon surrounding the bond areas occurred in the process.

During the bonding process, mechanical alignment using precise diameterpins were applied to ensure controlled processing and prevent shatteringof the fragile thin cantilevers. The bonded pair of cantilevers (71-72)are now ready for deposition of the SMA thin films (78-79).

The SMA thin films are composed of Ni--Ti--Cu deposited using a mixed dcmagnetron sputtered deposition, the details of the mixed sputteringprocess are set forth in copending application Ser. No. 08/(IL-9463),filed May 1995, entitled, "Multiple Source Deposition Of Shape-MemoryAlloy Thin Films" and assigned to the assignee of this application. Inthat sputtering process, three (3) separate targets are used to sputterthe alloy such that the power can be individually controlled to activelydetermine the alloy composition. The thin film was deposited at 505° C.,for example, so that it is in situ annealed to relieve the residualstress. The SMA film was initially deposited sequentially on the outersides or surface of the cantilever arms (71-72) of FIG. 7, for example,so that one side is annealed twice at 505° C., but preferably depositionof the SMA film prior to bonding of the cantilever arms would reducethermal stress in the film. The following sets forth a concise processsequence for fabricating a micro-actuator, such as illustrated in FIG.7, the sequence includes:

a) pattern crystal plane test marks, align targets and alignment holes.

b) pattern saw cut channel guide lines.

c) pattern silicon etch channels following the (111) plane direction.

d) anisotropic etching of the silicon etch channels by KOH.

e) shadow mask alignment to wafer, and deposition of Ti/Au film.

f) mechanical pin alignment and eutectic bonding at 380° C. (3 min.) and10⁻⁴ Torr.

g) magnetron sputter deposition of Ni--Ti--Cu films on both sides within situ annealing at 505° C.

h) dice up individual microgrippers.

The microgripper of FIG. 7, is actuated using the dc magnetron sputterednickel-titanium-copper-shape memory film. Shape memory actuation isbased on a crystalline phase transformation in which the low temperaturephase (martensite) is easily and reversibly deformable via twins, whilethe high temperature phase (austenite) has one rigid configuration. TheNi₄₂ Ti₅₀ Cu₈ alloy transforms just above body temperature (37° C.),making it useful for implantable medical devices, and has a narrowerhysteresis than binary nickel-titanium which increases efficiency andimproves response time. Furthermore, the addition of copper makes thetransformation temperature less sensitive to film composition.

In the microgripper application, actuation occurs by the recovery oftensile residual stress in the memory film, the data thereof beingobtained by measuring substance curvature as a function of temperature.The film, which is deposited at 500° C., develops a tensile thermalstress as it is cooled after deposition. When cooled below thetemperature at which the martensitic transformation starts, the thermalstress in the film can relax by twin-related deformation. This tensilethermal stress can be recovered by heating the film. Thus, the siliconmicrogripper cantilevers act as bias springs which are opened by thecontracting shape-memory film (78-79) when heated, then deflected backto a neutral position and stretch the shape-memory film when cooled.Films with up to 500 MPa recoverable stress have been deposited, but thefilm on the cantilevers of FIG. 7, for example, have a recoverablestress of 375 MPa. Testing of the stress induced by the Ni--Ti--Cu filmwas measured by a Tencor FLX-2320 laser system, which measures thecurvature induced by the film on an Si substrate, which is translatedinto stress.

In order to evaluate the gripping force induced by the Ni--Ti--Cu SMAfilm, an equivalent model with an opening force at the tip was assumed.By applying bimetallic stress equations, the relation between theNi--Ti--Cu film stress and the deflection of the gripper tip wascalculated. For a film thickness of 5 μm, the deflection is calculatedto be 53 μm. Experimental results showed the gripper opening to 55 μmwhen fully actuated. Using the equivalent model, it was found that itrequires 20 mN to deflect the microgripper to 55 μm. Therefore, agripping force of 40 mM (20 mN on each cantilever) is applied for afully open microgripper.

The heating of the microgripper of FIG. 7 was applied by an integratedcircuit (IC) fabricated thin film resistor heater pad, as described ingreater detail with respect to FIGS. 10 and 11. The heater pad is placedon the microgripper cantilevers and current is applied, the heat istransferred from the heater to the Si gripper cantilevers for phasetransformation in the Ni--Ti--Cu film to take place. Thus, remote activeheating of the SMA film can be accomplished.

Also, the microgripper of FIG. 7 is being integrated with strain sensorfor feedback control as described hereinafter with respect to FIG. 12.

FIGS. 9, 9A and 9B illustrate packaging of the microgripper of FIG. 7 ona catheter. Components similar to those of FIG. 7 are givencorresponding reference numerals. The microgripper 70 is electricallyconnected to a wiring jacket 81 via a SMA film resistive heater,generally indicated at 90 on cantilever 71 and having contract pads 91and 92, which are connected via leads 93 and 94 to contact pads 95 and96 on conductive films 97 and 98 such as copper, bonded to a polymidemember 99, of an electrical feedthrough ribbon generally indicated at100. As indicated by leads 93' and 94', an identical resistive heaterand electrical connection arrangement is provided between cantilever 72of microgripper 70 and the conductive film on polymide member 99' ofwiring jacket 81. The polymide members 99 and 99' and associated copperfilms are connected to insulated feedthrough wires 101/102 and 101'/102'of ribbon 100, and are located within a catheter tube 103 (see FIG. 9A).The polymide members 99 and 99' include protruding end sections 104 and104' which, as indicated by the arrows 105, extend into the hollowchannel 80 of microgripper 70. The wiring jacket 81 is secured tomicrogripper 70 by a heat shrink tube 106 (see FIG. 9B).

The resistive heaters 90° of FIG. 9 located on cantilevers 71 and 72 ofthe microgripper 70 may be of the type illustrated in FIGS. 10, 10A and10B or of the type illustrated in FIGS. 11, 11A and 11B, each havingpiezoresistive feedback capabilities.

In the FIG. 10 embodiment, the resistive heater 90 includes contact pads91 and 92, as in FIG. 9, with resistive wires 107 being in electricalcontact with pad 91 and resistive wires 108 being in contact with pad92. FIG. 10A is a greatly enlarged section of FIG. 10 and composed of asilicon beam (cantilever 71), SMA resistive wires 107, 108, 107, ofresistive heater 90, between which are layers 109 and 110 of an oxide,on top of which are layers 111 and 112 of polysilicon (poly-Si), and ontop of which are sections of the SMA thin film 78, covered by an oxideor protective layer 113. FIG. 10B is an enlarged cross-sectional sideview of the FIG. 10 embodiment.

The resistive heater 90 of FIGS. 11, 11A and 11B is generally similar tothe FIG. 10 embodiment, and similar reference numbers will be utilized.In FIG. 11, the resistive heater 90 includes contact pads 91 and 92,with resistive wires 107 connected to pad 91 and resistive wires 108connected to pad 92, as in the FIG. 10 embodiment. FIG. 11A is a greatlyenlarged view of a section of FIG. 11 and composed of a silicon beam(cantilever) 71, an oxide layer 114, a pair of polysilicone (poly-Si)layers 115 and 116 on which is deposited oxide (LTO) layers 117 and 118,the SMA thin film 78 and an oxide or protective layer 113. FIG. 11B isan enlarged cross-sectional side view of the FIG. 11 embodiment.

FIG. 12 schematically illustrates a force feedback control of themicrogripper 70 of the FIG. 7 embodiment, and similar components aregiven corresponding reference numerals. A sensing film 120 is depositedon a cantilever 71 and is connected via a strain-to-stress conversion,indicated at 121, as discussed above, to a specified force indicator122, the output of which is directed through signal processor(amplifier) 123 to an actuation film (SMA film 78). While not shown, thelower cantilever 72 is provided with a similar arrangement.

The FIG. 7 embodiment can be modified to provide a hydraulicpressure/fluid delivery system, as illustrated in FIG. 13. Here,cantilevers 125 and 126 of a microactuator 70' are provided with SMAthin films 127 and 128, respectively, with cantilevers 125 and 126 beingconnected by a section 129 having an opening, not shown, therein. Amicroballoon 130 is position intermediate one end 131 and 132 ofcantilevers 125 and 126, while the other end 133 and 134 thereof isprovided with grippers or jaws 135 and 136. Upon actuation, ends 131/132of the cantilever move inwardly, as indicated by the arrows, while theends 133 and 134 move outwardly, as indicated by the arrows, wherebyfluid within the microballoon 130 is forced therefrom as indicated bythe arrows 137, thereby delivering the fluid 137 to a point of use.

It has thus been shown that the present invention provides anelectromechanical micromechanism (either IC silicon-based or precisionmicromechanical) which will, for example, extend and improve theapplication of catheter-based interventional therapies for the repair ofarterio-aneurysms in the brain or other interventional clinicaltherapies. The microgripper of this invention, in addition to medicalapplications, has non-medical uses, such as micro assembling and forremote and precise manipulation of small objects, and has the capabilityto operate in small areas having 250 μm diameters, such as small bloodvessels.

While particular embodiments, materials, parameters, etc., having beenset forth to exemplify the invention, such are not intended to belimiting. Modifications and changes may become apparent to those skilledin the art, and it is intended that the invention be limited only by thescope of the appended claims.

We claim:
 1. A micro-mechanical system, comprising:a catheter having adistal end for insertion into and manipulation within a body and a nearend providing for a user to control said manipulation of said distal endwithin said body; a fiberoptic cable disposed within the catheter andhaving a distal end proximate to said distal end of the catheter and anear end for external coupling of-laser light energy; a microgripperattached to said distal end of the catheter and providing for thegripping or releasing of an object within said body; and alaser-light-to-mechanical-power converter connected to receive laserlight from said distal end of the fiberoptic cable and connected tomechanically actuate the microgripper.
 2. The micro-mechanical system ofclaim 1, further comprising:an electronic sensor connected to receiveelectrical power from said distal end of the fiberoptic cable andconnected to provide signal information about a particular physicalenvironment in which the microgripper is located and externallycommunicated through the fiberoptic cable to a user.
 3. Themicro-mechanical system of claim 2 wherein:the sensor detects at leastone of gap distance, pH, chemistry, position, acceleration, pressure,temperature, ambient light, ambient sound, and video image.
 4. Themicro-mechanical system of claim 1, further comprising:a mechanicalsensor attached to said distal end of the fiberoptic cable and connectedto provide light signal information about a particular physicalenvironment in which the microgripper is located and externallycommunicated through the fiberoptic cable to a user.
 5. Themicro-mechanical system of claim 4 wherein:the sensor detects at leastone of gap distance, pH, chemistry, position, acceleration, pressure,temperature, ambient light, ambient sound, and video image.
 6. Themicro-mechanical system of claim 1, wherein:thelaser-light-to-mechanical-power converter includes a photo-voltaic cellthat generates electrical power in response to laser light received bythe fiberoptic cable and further includes an electromechanical motormechanically connected to actuate the microgripper.
 7. Themicro-mechanical system of claim 1, wherein:thelaser-light-to-mechanical-power converter includes a heat-sensitivephoto-thermal material mechanically connected to actuate themicrogripper in response to laser light received by the fiberoptic cableat said near end and conducted to said distal end.
 8. Themicro-mechanical system of claim 1, wherein:thelaser-light-to-mechanical-power converter includes a capacitorelectrically connected to discharge into an electromechanical motor inresponse to laser light received by the fiberoptic cable at said nearend and conducted to said distal end, and wherein, saidelectromechanical motor is mechanically connected to actuate themicrogripper.